Study of iron and aluminum binding to Suwannee River fulvic acid using absorbance and fluorescence spectroscopy: Comparison of data interpretation based on NICA-Donnan and Stockholm humic models

International audienceThis study examined the evolution of absorbance and fluorescence spectra of standard Suwannee River fulvic acid (SRFA) induced by its interactions with iron and aluminum. The results show that changes of SRFA absorbance are associated with a consistent response of the carboxylic and phenolic functional groups to iron and aluminum forming bonds with these groups, and their deprotonation induced by such binding. The observed changes of SRFA absorbance were quantified via the use of DSlope(325-375) parameter that determines the behavior of the slope of logarithms of SRFA absorbance in the range of wavelengths 325 -375 nm in the presence of varying concentrations of iron or aluminum. DSlope(325-375) values were correlated linearly with the concentration of SRFA-bound iron and aluminum determined using either NICA-Donnan or Stockholm Humic Model (SHM) but the correlation was stronger for the former model (R-2 > 0.98). The slopes of these correlations were similar for both iron and aluminum concentrations